Broadband waveguide with means for suppressing te {11 {11 mode

ABSTRACT

A rectangular waveguide dimensioned to propagate the TE10 mode includes at each end of the waveguide terminations for terminating the TE20 mode comprising slotted tapered ridges with lossy cavities closing the slots.

United States Patent Parisi Sept. 10, 1974 [54] BROADBAND WAVEGUIDE WITHMEANS 3,157,845 11/1964 White 333 34 FOR SUPPRESSING TEZDMODE 3,218,58611/1965 Khoury 333/98 M f 3,508,175 4/1970 Alford 333/34 Inventor: FrankE-Par11,Wa1tham,MaSS- 3,539,951 11/1970 Tischer 333/34 73 Assi ee:Adams-Russell Co. Inc. Waltham, 1 gn Mass, Primary ExaminerArch1e R.Borchelt Assistant ExaminerWm. H. Punter [22] Filed: Apr. 20, 1973Attorney, Agent, or FirmCharles Hieken, Esq.; Jerry 21 Appl. No.:352,925 Cohen, q-

52 us. (:1. 333/98 M, 333/34 [57] f 51 Int. Cl. 1101 1/16, HOlp 5/03 Arectangular wevegulde dlmenslened to propagate [58] Field of Search333/98 M, 34 the m mode includes at eeeh end of the waveguideterminations for terminating the TE20 mode compris- [5 References Citeding slotted tapered ridges with lossy cavities closing UNITED STATESPATENTS 2,869,085 1/1959 Pritchard et a]. 333/98 M 8 la ms, 3 DrawingFigures BROADBAND WAVEGUIDE WITH MEANS FOR SUPPRESSING TE MODEBACKGROUND OF THE INVENTION The present invention relates to broadbandwaveguides and more particularly concerns a novel broadband waveguidecapable of efficiently transmitting microwave power over a relativelybroad range of frequencies while avoiding overly critical dimensiontolerances. The invention suppresses the undesired TE mode withoutappreciably affecting the desired TE mode. v

It is usually preferred to operate a rectangular waveguide in the TEmode in which the electric field is parallel to the narrow walls with amaximum midway .between them. A serious limitation for broadbandoperation is the occurrence of the TE mode in which the electric fieldis also parallel to the narrow walls but is zero both at the center andthe narrow walls and oppositely phased in the two halves of the guide.In terms of results, the transmission loss characteristic of arectangular waveguide is characterized by spikes at frequencies wherethe TE mode becomes significant. One approach to suppressing the TB modeis to form the top and bottom broad walls with lengthwise slots midwaybetween the narrow walls, thereby interrupting the current for the TEmode without disturbing the TE mode because the current for the lattermode is zero there. Radiation will occur from the slot, but theradiation may be reduced by backing the slot with a cavity having lossymaterial. This approach is costly, complicated and presents especiallygreat problems when the waveguide must follow a number of bends andtwists.

A ridged waveguide may be used for propagating a broad band of microwavefrequencies; however, such waveguides have a number of disadvantages.Dimensions are more critical and losses relatively high. Moreover, therelatively close spacing in the ridge region limits the amount of powerthat may be transmitted. The criticality of dimensions is an especiallyserious problem when the waveguide must follow a number of twists andbends.

Accordingly, it is an important object of the invention to provide abroadband rectangular waveguide that eliminates one or more of thedisadvantages enumerated above.

It is a further object of the invention to achieve the preceding objectwith a rectangular waveguide capable of efficiently transmittingmicrowave energy over a broad range of frequencies over a relativelylong path that may include a number of twists and bends.

It is still a further object of the invention to achieve one or more ofthe preceding objects with structure that is relatively free fromcomplexity.

It is a further object of the invention to achieve one or more of thepreceding objects with negligible leakage radiation.

SUMMARY OF THE INVENTION According to the invention, a rectangularwaveguide includes means at least at one end for terminating the TEmode, preferably comprising slotted tapered ridges with lossy cavitiesclosing the slot in a section that also matches a ridged waveguide tothe rectangular waveguide.

Numerous other features, objects and advantages of the invention willbecome apparent from the following specification when read in connectionwith the accompanying drawing in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top view of an embodimentof the invention;

FIG. 2 is a transverse section through section 22 of FIG. 1; and

FIG. 3 is a longitudinal section through section 33 of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference now to thedrawing and more particularly FIG. 1 thereof, there is shown a top viewof a waveguide according to the invention. A long run of rectangularwaveguide 11 is coupled to short runs of double ridged waveguides 12 and13, respectively, by identical transition sections 14 and 15 havingcentral longitudinal slots 16 and 17, respectively, filled with taperedwedges of lossy material 18 and 19, respectively. for dissipating energyin the TE mode covered by mating conducting plates 18' and 19',respectively.

Referring to FIG. 2, there is shown a view through section 22 of FIG. 1.The transition section 14 includes upper and lower gradually taperingridges 21 and 22, respectively, with upper ridge 21 formed with the slot16 for interfering with the current in the TE; mode without appreciablyaffecting the current in the TE mode. While only an upper slot 16 isshown, there could be a lower slot if desired in a particular situation.

Referring to FIG. 3, there is shown a longitudinal sectional viewthrough section 33 of FIG. 1 illustrating how tapered ridges 21 and 22taper from zero depths at a rectangular waveguide 11 to a depthcorresponding to the depth of the ridges in double-ridged waveguide 12.

Having generally described a preferred embodiment of the invention,certain preferred dimensions will be defined. If the width of therectangular guide is a and the height b, a z 2 \/2b. The transitionsection is typically a wavelength or more at the lowest frequency of therange to be transmitted. The ridge elements are tapered because a TEwave should preferably not see an abrupt change. The slot depth istapered from zero to max so a TE, wave preferably sees no abrupt change.The lossy cavities are typically substantially the same length as theslots. The slot length is typically greater than a wavelength at the lowfrequency end of the band to be propagated. The slot width is less thanthe ridge width, typically 20 percent of the ridge width. The ridgewidth is typically a/4. Those skilled in the art may use varioustechniques to minimize the VSWR over the frequency range of interest.The invention may typically intercouple RG52 rectangular waveguide withWRD 750 D24 ridged waveguide.

While the tapered transition section is preferred to provide a goodmatch between ridged and rectangular waveguides for the TE mode, theprinciples of the invention may be embodied with a direct connectionbetween the ridged and rectangular guides. At least one of the ridgeswould be slotted for a wavelength or more from the junction with therectangular guide at the lowest frequency to be transmitted and backedby a lossy cavity.

The specific structure described herein is only by way of example forillustrating the best mode now contemplated for practicing theinvention. Those skilled in the art may use other techniques forattenuating the TE mode at each end of the rectangular waveguide withinthe principles of the invention. Since those skilled in the art may nowmake numerous other uses and modifications of and departures from thespecific embodiments described herein, the invention is to be construedas embracing each and every novel feature and novel combination offeatures present in or possessed by the apparatus and techniques hereindisclosed and limited solely by the spirit and scope of the amendedclaims.

What is claimed is:

l. Waveguide apparatus comprising,

a rectangular waveguide dimensioned to propagate energy in the TE, modeover a predetermined frequency range,

at least one other waveguide coupled to one end of said rectangularwaveguide,

and means coupled to said one end for attenuating the TE mode with saidfrequency range without appreciably affecting the transmission of the TEmode,

said at least one other waveguide comprising a ridged waveguide and saidmeans coupled to said one end comprising a tapered rectangular waveguidesection formed with a tapered slotted central ridge intercoupling saidrectangular waveguide and said ridged waveguide with lossy materialcoupled to the slot in said tapered slotted central ridge.

2. Waveguide apparatus in accordance with claim 1 and furthercomprising,

a ridged waveguide coupled to the other end of said rectangularwaveguide,

and means coupled to said other end of said rectangular waveguide forattenuating said TE mode without appreciably affecting the transmissionof the TE mode.

3. Waveguide apparatus in accordance with claim 1 wherein said meanscoupled to said one end comprises said slot adjacent to said one endlongitudinally and symmetrically aligned in the broad wall of awaveguide coupling section substantially where the TE mode current is amaximum.

4. Waveguide apparatus in accordance with claim 1 wherein said lossymaterial fills said slot for dissipating energy in said TE mode.

5. Waveguide apparatus in accordance with claim 1 wherein the length ofsaid slot is greater than a wavelength at the low frequency end of saidpredetermined frequency range.

6. Waveguide apparatus in accordance with claim 5 wherein the width ofsaid slot is substantially 20 percent of the width of said ridge.

7. Waveguide apparatus in accordance with claim 6 wherein the width ofsaid ridge is substantially onefourth the width of said rectangularwaveguide.

8. Waveguide apparatus in accordance with claim 7 wherein said lossymaterial substantially fills said slot for dissipating energy in saidTE- mode.

1. Waveguide apparatus comprIsing, a rectangular waveguide dimensionedto propagate energy in the TE10 mode over a predetermined frequencyrange, at least one other waveguide coupled to one end of saidrectangular waveguide, and means coupled to said one end for attenuatingthe TE20 mode with said frequency range without appreciably affectingthe transmission of the TE10 mode, said at least one other waveguidecomprising a ridged waveguide and said means coupled to said one endcomprising a tapered rectangular waveguide section formed with a taperedslotted central ridge intercoupling said rectangular waveguide and saidridged waveguide with lossy material coupled to the slot in said taperedslotted central ridge.
 2. Waveguide apparatus in accordance with claim 1and further comprising, a ridged waveguide coupled to the other end ofsaid rectangular waveguide, and means coupled to said other end of saidrectangular waveguide for attenuating said TE20 mode without appreciablyaffecting the transmission of the TE10 mode.
 3. Waveguide apparatus inaccordance with claim 1 wherein said means coupled to said one endcomprises said slot adjacent to said one end longitudinally andsymmetrically aligned in the broad wall of a waveguide coupling sectionsubstantially where the TE20 mode current is a maximum.
 4. Waveguideapparatus in accordance with claim 1 wherein said lossy material fillssaid slot for dissipating energy in said TE20 mode.
 5. Waveguideapparatus in accordance with claim 1 wherein the length of said slot isgreater than a wavelength at the low frequency end of said predeterminedfrequency range.
 6. Waveguide apparatus in accordance with claim 5wherein the width of said slot is substantially 20 percent of the widthof said ridge.
 7. Waveguide apparatus in accordance with claim 6 whereinthe width of said ridge is substantially one-fourth the width of saidrectangular waveguide.
 8. Waveguide apparatus in accordance with claim 7wherein said lossy material substantially fills said slot fordissipating energy in said TE20 mode.